Methods for making coated threaded metallic

Abstract

Methods for coating threaded metallic pieces which include using a threaded metallic piece as a cathode of an electrolytic cell in a bath which includes Zn ion and whereby electro-deposition of a first layer containing Zn takes place followed by deposition of a second layer of a polyester-based paint are provided. Such processes are especially useful for components of the automobile industry, such as wheel screws.

1 . A method for coating a threaded metallic piece, comprising:
 providing a bath which comprises Zn ions,   introducing the metallic piece into the bath, wherein the metallic piece acts as a cathode of an electrolytic cell and wherein electro-deposition of a first layer comprising Zn is brought about on the surface of the metallic piece, and   applying on the piece coated by the first layer a second layer of a polyester-based paint.   
     
     
         2 . The method of  claim 1 , wherein the electrolytic cell comprises membranes screening the electrodes. 
     
     
         3 . The method of  claim 1 , wherein the bath further comprises Ni ions and wherein the first layer comprises Zn and Ni. 
     
     
         4 . The method of  claim 1 , wherein the metallic piece is subjected to treatments of degreasing and/or pickling prior to the electro-deposition. 
     
     
         5 . The method of  claim 1 , wherein the metallic piece is subjected to a treatment of passivation after the electro-deposition and prior to the application of the second layer of paint. 
     
     
         6 . The method of  claim 1 , wherein the second layer of paint is applied in two coats. 
     
     
         7 . The method of  claim 6 , wherein the application of each coat of paint comprises immersing the metallic piece in a bath of paint, centrifuging and baking. 
     
     
         8 . The method of  claim 1 , wherein the metallic piece is a wheel screw. 
     
     
         9 . The method of  claim 1 , wherein the first layer has a thickness between about 8 and about 12 μm, and the second layer has a thickness between about 11 and about 14 μm. 
     
     
         10 . The method of  claim 1 , wherein the paint comprises a black pigment.